<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8" />
    <meta http-equiv="X-UA-Compatible" content="IE=edge" />
    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
    <title>Document</title>
  </head>
  <body>
    <input type="text" id="username" /><input
      type="checkbox"
      id="remember"
    />记住用户名
    <script>
      var username = document.querySelector("#username");
      var remember = document.querySelector("#remember");
      if (localStorage.getItem("username")) {
        username.value = localStorage.getItem("username");
        remember.checked = true;
      }
      remember.addEventListener("change", function () {
        if (this.checked) {
          localStorage.setItem("username", username.value);
        } else {
          localStorage.removeItem("username");
        }
      });
    </script>
  </body>
</html>
